Process for making encapsulated anchor rung

ABSTRACT

A climbing rung for anchoring to the wall of a manhole shaft. The climbing rung has a generally U-shaped core of two parallel legs spaced apart by a central tread. Each leg is sheathed in a pre-formed protective sleeve, closed at one end, by inserting the leg into the mouth of the sleeve. An injection moulded protective coating is bonded to the core of the tread and the core of each leg, extending to proximate the mouth of each pre-formed sleeve when a leg is sheathed therein, forming a sealing interface proximate the annular lip circumferentially defining the mouth of each sleeve. A method includes gripping the climbing rung only proximate the pre-formed protective sleeves when both legs are sheathed therein, so as to permit positioning the core of the tread and legs, extending only to proximate the mouth of each pre-formed protective sleeve, in an injection moulded cavity radially spaced equidistant the surface of the mould cavity. Advantageously, positioning pins inside the injection mould cavity for radially spacing the core of the climbing rung from the surface of the mould cavity are thereby not required. The method also includes alternatively gripping at least two oppositely spaced portions of the core of the climbing rung and alternately coating the portion of the climbing rung opposite the end which is being gripped.

FIELD OF INVENTION

The present invention relates to an improved climbing rung encapsulatedin a corrosion resistant material for anchoring to the wall of a manholeshaft and an improved method of making same.

BACKGROUND OF INVENTION

Climbing rungs for anchoring to the wall surface of a manhole shaft areknown, employing a generally U-shaped aluminum or steel rung consistingof two parallel legs for anchoring on the wall spaced apart by a centraltread. The two parallel anchoring legs are to be permanently insertedinto receptive bore holes in the wall.

It is recognized by those skilled in the art that a manhold shaft is acorrosive environment presenting the risk of rusting or corrosion ofsteel or aluminum climbing rungs when they are anchored into a wall.Accordingly a variety of coatings and combinations thereof have beenproposed for protecting the aluminum or steel `core` of the step againstcorrosion. For example the `core` may be sheathed in a pre-formedprotective jacket or sleeve open at both ends. A pair of pre-formedprotective anchor sleeves, each one sealed at a conically tapered endfor insertion into a receptive bore hole in the wall are adapted to fitover the ends of the anchoring legs and overlap the protective jacketsheathing the `core` of the climbing rung. Exposure of the `core` tocorrosive substances is thereby mitigated. However a perfect seal is notachieved --use of the climbing rung will result in flexion and vibrationspreading corrosive substances along the cylindrical seams between theanchor sleeve, protective jackert or sleeve and `core`. The resultingrust and corrosion underneath the anchor sleeves and protective jacketis not visible to inspection.

Many building codes now require that protective coatings provide a bondencapsulating the `core` of the climbing rung sufficient that currentwill not be conducted from the `core` through the protective coating toelectrical ground. The response to the need for a more effective meansof sealing the `core` has been to encapsulate it in a corrosionresistant material such as recovered battery case material by means ofan injection moulding process. According to this process the entireclimbing rung is placed in the cavity of a mould body and moltenpolyethylene or the like is injected into the mould cavity. Usually the`core` is hollow inside. It is therefore necessary to plug the ends ofthe `core` to prevent the molten polyethylene from being injected intothe `core`. Since the contact between the climbing rung and the side ofthe mould cavity will preclude the injected polyethylene from forming acoat of uniform thickness it is necessary to support the climbing rungcentrally in the mould cavity. To this end, typically pins are providedwhich project into the mould cavity to support and evenly space theclimbing rung from the surface of the mould cavity. After the climbingrung is ejected from the mould body, holes are left in the coatingproximate the site where the support pins have contacted the `core`,which must be detected and filled. Plugging the ends of the `core` andfilling the pin holes adds to the cost of, and time needed, forproduction. In another embodiment it has been taught to provide supportpins that `float` in bore holes in the body of the mould under airpressure less than the injection pressure and which normally projectinto the mould cavity. When the ejection half and the injection half ofthe mould are joined, the support pins extend into the mould cavity tocentrally support the climbing rung. As the injection pressure becomesgreater than the air presssure `floating` the support pins in the boreholes, the pins retract from the mould cavity into the body of themould. Since polyethylene can leak into the bore holes under pressure,the fit of the support pins in the bore holes requires a tolerance of0:0. Moulds having such tolerances are expensive to manufacture. Inpractice the pins get stuck and fail to retract. Therefore a hole mayunexpectedly be left in the injection moulded coating which must bedetected and filled, resulting in high rejection rates and lowproductivity. Accordingly, in practice such a system has an extremelylow production rate and is prone to failure.

It is therefore an object of this invention to provide an improvedclimbing rung having a combination of protective coatings sealing the`core` sufficient that electrical current will not be conducted throughthe protective coatings to electrical ground.

It is a further object of this invention to provide an improved methodof encapsulating the core of a climbing rung in an injection mouldingprocess.

Further and other objects of the invention will be apparent to thoseskilled in the art from the following Summary of the Invention andDetailed Description of Embodiments thereof.

SUMMARY OF INVENTION

According to one aspect of the invention there is provided an improvedclimbed rung comprising in combination a generally U-shaped core havingtwo parallel legs spaced apart by a central tread, each leg sheathed ina pre-formed protective sleeve open at one end to receive the leg andsealed at the opposite end for insertion into a receptive bore hole in awall; and, a protective coating bonded to the climbing rung andpre-formed protective sleeves by means of an injection moulding process,the injection moulded protective coating encapsulating the tread andlegs of the climbing rung extending only to proximate the receptive endof each pre-formed protective sleeve melding with the annular lip ofeach pre-formed protective sleeve proximate the receptive end forming asealing interface thereat sufficient that electric current will not beconducted, from the core through the protective coating comprising thecombination in a sealing interface of a pair of pre-formed protectivesleeves and an injection moulded protective coating, to electricalground.

According to a preferred embodiment of the invention each pre-formedprotective sleeve proximate the annular lip of the receptive end thereofis of an inside diameter slightly greater than the outside diameter ofthe core of each leg so as to provide an annular pocket into which thepolyethylene may weep under normal injection pressure. Preferably eachpre-formed protective sleeve proximate the outside circumferentialportion of the annular lip at the receptive end thereof is slightlyangularly tapered radially inward. All that is necessary is that thepre-formed protective sleeve meld with the injection moulded protectivecoating proximate the annular lip of the respective end thereof in asealing interface.

According to another aspect of the invention there is provided animproved method of manufacturing a climbing rung in a mould body havingan ejection half and an injection half, the climbing rung having agenerally U-shaped core of two parallel legs spaced apart by a centraltread encapsulated in a protective coating comprising the combination ina sealing interface of a pair of pre-formed protective sleeves and aninjection moulded protective coating, the method comprising the steps of(a) sheathing the end of each leg in a pre-formed protective sleeve openat one end to receive the leg; (b) gripping the pre-formed protectivesleeves with means for gripping the climbing rung only proximate the endof each leg; (c) positioning with the gripping means the tread and legsof the climbing rung extending only to proximate the receptive end ofeach pre-formed protective sleeve centrally in a disjointed injectionmould cavity; d) closing the ejection half and the injection half of themould body so as to form the mould cavity enclosing the tread and legsof the climbing rung extending only to proximate the receptive end ofeach pre-formed protective sleeve, the mould body forming an annularseal at the outside circumference of each pre-formed protective sleeveproximate the receptive end; e) injecting a molten thermoplasticmaterial into the mould cavity whereby the material flows into theentire mould cavity evenly coating the core of the climbing rung andweeping into the interface at the receptive end of each pre-formedsleeve and each leg, whereby the injected thermoplastic material meldswith the pre-formed protective sleeves to form a sealing interface.

According to a preferred embodiment of the invention there is providedan improved method of manufacturing a climbing rung in a mould bodyhaving an ejection half and an injection half, the climbing rung havinga generally U-shaped core of two parallel legs spaced apart by a centraltread encapsulated in a protective coating comprising the combination ina sealing interface of a pair of pre-formed protective sleeves and aninjection moulded protective coating each sleeve having an annular spacebetween the receptive end of said sleeve and the outside annularcircumference of each leg, the method comprising the steps of (a)sheathing the end of each leg in a pre-formed protective sleeve open atone end to receive the leg; (b) gripping the pre-formed protectivesleeves with means for gripping the climbing rung only proximate the endof each leg; (c) positioning with the gripping means the tread and legsof the climbing rung extending only to proximate the receptive end ofeach pre-formed protective sleeve centrally in a disjointed injectionmould cavity; (d) closing the ejection half and the injection half ofthe mould body so as to form the mould cavity enclosing the tread andlegs of the climbing rung extending only to proximate the receptive endof each pre-formed protective sleeve, the mould body forming an annularseal at the outside circumference of each pre-formed protective sleeveproximate the receptive end; (e) injecting a molten thermoplasticmaterial into the mould cavity whereby the material flows into theentire mould cavity evenly coating the core of the climbing rung andweeping into the annular space between the receptive end of eachpre-formed sleeve and the outside annular circumference of each leg andover the annular lip of the receptive end of each pre-formed sleeve, andwhereby the injected thermoplastic material melds with the pre-formedprotective sleeves to form a sealing interface.

According to another aspect of the invention there is provided animproved method of manufacturing an encapsulated climbing rung in amould body having an ejection half and an injection half, the climbingrung having a generally U-shaped core of two parallel legs spaced apartby a central tread encapsulated in a protective coating, the coatingincluding the combination in a sealing interface of (i) a pair ofinjection moulded protective sleeves encapsulating the portion of eachleg extending from the end thereof to a position intermediate the end ofeach leg and the central tread, and (ii) an injection moulded protectivecoating encapsulating the tread extending to the sealing interfaceproximate the annular end of each injection moulded protective sleeveremote from the end of each leg; the method comprising the steps of: (1)gripping with gripping means, alternately one portion and then anoppositely spaced portion of the core of the climbing rung remote aportion of the core to be positioned with the gripping means centrallyin an injection mould cavity; by first (b) encapsulating one portion ofthe core of the climbing rung thus defining an annular encapsulated endthereof when the opposite portion of the climbing rung is gripped byremotely spaced gripping means; (c) then gripping the most recentlyencapsulated portion of the climbing rung and encapsulating theoppositely spaced portion of the core of the climbing rung, the laterencapsulated portion melding in a sealing interface with the annular endof the previously encapsulated portion whereby by alternately grippingat least two oppositely spaced portions of the core of the climbing rungthe entire core of the climbing rung is coated in an injection mouldingprocess.

According to one aspect of the invention there is provided an improvedmethod of manufacturing an encapsulated climbing rung in a mould bodyhaving an ejection half and an injection half, the climbing rung havinga generally U-shaped core of two parallel legs spaced apart by a centraltread encapsulated in a protective coating, the coating comprising thecombination in a sealing interface of (i) a pair of injection mouldedprotective sleeves encapsulating the portion of each leg extending fromthe end thereof to a position intermediate the end of each leg and thecentral tread, and (ii) an injection moulded protective coatingencapsulating the tread extending to the sealing interface proximateannular end of each injection moulded protective sleeve remote from theend of each leg; the method comprising the steps of: (a) gripping thecore of the climbing rung with means for gripping the climbing rung onlyremote the end of each leg; (b) positioning with the gripping means theend of each leg of the climbing rung extending only to proximate theportion of each leg remote the end of each leg centrally in a disjointedinjection mould cavity; (c) closing the ejection half and the injectionhalf of the mould body so as to form the mould cavity enclosing the endof each leg of the climbing rung extending only to the portion of eachleg remote the end of each leg, the mould body remote the end of eachleg forming an annular seal at the outside circumference of the core ofeach leg of the climbing rung; (d) injecting a molten material such aspolyethylene or the like into the mould cavity enclosing the said endportion of each leg of the climbing rung whereby a pair of mouldedprotective sleeves are formed, each sleeve encapsulating the portion ofeach leg extending from the end thereof to the annular end of the sleeveat a position intermediate the end of each leg and the central tread;(e) ejecting the climbing rung comprising the injection mouldedprotective sleeves from the mould cavity and gripping the injectionmoulded protective sleeves with gripping means for gripping the climbingrung only proximate the end of each leg; (f) positioning, with thegripping means for gripping the climbing rung only proximate the end ofeach leg and the tread centrally in an injection mould cavity; (g)closing the ejection half and the injection half of the mould body so asto form the mould cavity enclosing the tread and each leg of theclimbing rung extending only to proximate the annular end of eachinjection moulded protective sleeve, the mould body forming an annularseal at the outside circumference of each injection moulded protectivesleeve proximate its annular end; (h) injecting the molten material suchas polyethylene or the like into the mould cavity whereby thepolyethylene flows into the mould cavity evenly encapsulating the coreof the climbing rung comprising the central tread and each leg of theclimbing rung extending to the annular end of each injection mouldedprotective sleeve and melding in a sealing interface with the annularend of each injection moulded protective sleeve.

According to an alternative aspect of the invention there is provided animproved method of manufacturing an encapsulating climbing rung in amould body having an ejection half and an injection half, the climbingrung having a generally U-shaped core of two parallel legs spaced apartby a central tread encapsulated in a protective coating, the coatingcomprising the combination in a sealing interface of (i) a pair ofinjection moulded protective sleeves encapsulating the portion of eachleg extending from the end thereof to a position intermediate the end ofeach leg and the central tread, and (ii) an injection moulded protectivecoating encapsulating the tread extending to the sealing interfaceproximate an annular end of each injection moulded protective sleeveremote from the end of each leg; the method comprising the steps of: (a)gripping the core of the climbing rung with means for gripping theclimbing rung only proximate the end of each leg; (b) positioning withthe gripping means the tread and each leg of the climbing rung extendingonly to proximate the portion of each leg remote the end of each legcentrally in a disjointed injection mould cavity; (c) closing theejection half and the injection half of the mould body so as to form themould cavity enclosing the tread and each leg of the climbing rungextending only to proximate the portion of each leg remote the end ofeach leg, the mould body forming an annular seal at the outsidecircumference of the core of each leg remote the end of each leg; (d)injecting a molten material such as polyethylene or the like into themould cavity whereby the polyethylene flows into the mould cavity evenlyencapsulating the core of the climbing rung comprising the central treadand the portion of each leg remote its end; (e) ejecting the climbingrung comprising the encapsulated tread and the portion of each legremote its end from the mould cavity and gripping the encapsulatedportion of the climbing rung with gripping means for gripping theclimbing rung only remote the end of each leg; (f) positioning, withgripping means for gripping the climbing rung only remote the end ofeach leg, the end of each leg of the climbing rung extending only toproximate the portion of each leg remote the end of each leg andproximate the injection moulded coating of the tread and the portion ofeach leg remote the end of each leg centrally in an injection mouldcavity; (g) closing the ejection half and the injection half of themould body so as to form the mould cavity enclosing the end of each legof the climbing rung extending only to proximate the portion of each legremote the end of each leg, the mould body forming an annular seal atthe outside circumference of the portion of the injection mouldedcoating remote the end of each leg; (h) injecting the molten materialsuch as polylethlene or the like into the mould cavity enclosing thesaid end portion of each leg of the climbing rung whereby a pair ofmoulded protective sleeves are formed, each sleeve encapsulating theportion of each leg extending from the end thereof to the annular end ofthe coating remote the end of each leg and melding in a sealinginterface with the annular end of the coating encapsulating each legremote its end.

The invention will now be illustrated with reference to the followingdrawings of an embodiment of the invention.

DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of climbing rungs anchored in a manholeshaft.

FIG. 2 is a perspective view of a portion of a climbing rung.

FIG. 3 is an anchoring leg of a climbing rung partially cut away in apartial view of a longitudinal section and a cross-section.

FIG. 4 is a perspective view of a climbing rung encapsulated in thecombination in a sealing interface of pre-formed protective sleeves andan injection moulded protective coating.

FIG. 5 is a perspective view of the ejection side of a mould bodyincluding means for gripping the legs of a climbing rung only proximatethe ends.

FIG. 6 is a perspective view of the injection side of the mould bodyseen in FIG. 5.

FIG. 7 is a close-up side view of the means for gripping the legs of aclimbing rung only proximate the ends seen in FIG. 5, in an ejectionposition.

FIG. 8 is a view of the gripping means seen in FIG. 7 in a retractedposition suitable for an injection phase.

FIG. 8A is a close-up view of the annular space formed between thesurface of the mold cavity and the outside circumferential portion ofthe annular lip.

FIG. 9 is frontal schematic view of an alternative embodiment of themould body seen in FIGS. 5, 6, 7 and 8, and a mould cavity thereincontaining a climbing rung, shown in one position for gripping theclimbing rung remote the end of each leg.

FIG. 10 is a frontal schematic view of the mould body shown in FIG. 9,shown in an alternative position for gripping the climbing rungproximate a pair of protective sleeves formed by injection moulding atthe end of each leg.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

With reference to FIG. 1 there is shown a plurality of encapsulatedclimbing rungs 9 anchored in a wall 11 of a manhold shaft.

Referring to FIGS. 2, 3 and 4 there is shown a climbing rung 9 having acore 10 (seen in FIG. 2) comprising two parallel core legs 13 spacedapart by a central tread 15. Each core leg 13 is sheathed in apre-formed protective sleeve 17 open at one receptive end 19 to receivethe leg 13. The opposite end is sealed 21, preferably conically taperedso as to be suitable for insertion into a receptive bore hole in theshaft wall 11. An injection moulded protective coating 23 is bonded tothe core 10 of the climbing rung comprising the central tread 15 andcore legs 13, and extends to proximate the receptive end 19 of eachpre-formed protective sleeve 17. Referring to FIG. 3 and 8A, the annularlip 25 of the respective end 19 of each sleeve 17 is of an insidediameter slightly greater than the outside diameter of each core leg 13so as to provide an annular pocket 27 proximate the inside circumferenceof the annular lip 25 into which the injection moulded protectivecoating 23 may weep under normal injection pressure. Preferably theannular lip 25 proximate the outside circumferential portion 29 thereofis slightly angularly tapered radially inward so as to provide anannular space 30 (best seen in FIG. 8) between the surface of a mouldcavity 32 and the outside circumferential portion 29 of the annular lip25, into which the polyethylene may weep under normal injectionpressure. All that is necessary is that the annular lip 25 of eachsleeve 17 and the injection moulded protective coating 23 meld togetherto form a sealing interface 31 (best seen in FIG. 3) proximate theannular lip 25.

With reference to FIGS. 2, 5, 6, 7 and 8 there is shown a method ofmanufacturing an encapsulated climbing rung 9, comprising the followingsteps: Each core leg 13 of the climbing rung core 10 is sheathed in apre-formed protective sleeve 17 by insertng the core leg 13 into thereceptive end 19 of the sleeve 17. Referring to FIGS. 5 and 6, a mouldbody 33 comprising an ejection half 35 and an injection half 37,symmetrically opposed and conjoinable one to the other is provided. Theejection half 35 of the mould body 33 has a receptive bore 39 (best seenin FIGS. 7 and 8), the receptive bore 39 for receiving the sleeves 17when the core legs 13 are sheathed therein. The receptive bore 39 iscarried by an ejection system 41 that is capable of retracting 43. Afterthe unfinished rung 10, 13 is placed in the receptive bores 39, theejection system 41 retracts 43 into the ejection half 35 of the mouldbody 33 so as to evenly space the core 10 from the surface 45 of theejection side of the mould cavity 32a. A locating pin 47 (best seen inFIGS. 7 and 8) is provided at the bottom of each receptive bore 39 so asto permit height adjustment of each sleeve 17 in relation to the twosealing collars 49. The sealing collars 49 each comprise two halves 49a,49b, one half 49a seated at the base of the ejection half of the mouldcavity 32a; the other half 49b seated at the base of the injection halfof the mould cavity 32b.

After the ejection system 41 has retracted 43 into the ejection half 35of the mould body 33 the symmetrically opposed injection half 37 of themould 33 is joined therewith so as to form a mould cavity 32 comprisedof the ejection side of the mould cavity 32a and the injection side ofthe mould cavity 32b, thereby positioning the tread 15 and core legs 13extending only to proximate the annular lip 25 of each sleeve 17radially equidistant to the surface 45 of the mould cavity 32. In theclosed position of the mould 33, best seen in FIG. 8, the two sealingcollars 49 form an annular seal about the outside circumference of eachsleeve 17 proximate the receptive ends 19. Preferably the sealingcollars 49 are positioned slightly below the annular lip 25 of eachsleeve 17.

Referring to FIG. 6 and 8A, the injection half 37 of the mould body 33is provided with a sprue 51 supplying molten polyethylene or the like toa runner 53. The molten polyethylene enters the mould cavity 32 throughthe runner gates 55, flowing into the entire mould cavity 32 evenlycoating the core 10 and weeping into the annular pocket 27 and annularspace 30, thereby melding with each pre-formed protective sleeve 17proximate the annular lip 25 thereof to form a sealing interface 31. Themould halves 35,37 may then separate; the ejection system 41 will ejectfrom the ejection half 35 of the mould, and an operator may then liftthe completed rung up from out of the receptive bores 39.

With reference to FIGS. 9 and 10 there is shown an alternative method ofmanufacturing the encapsulated climbing rung 9 without using thepre-formed protective sleeves 17. There is also shown an alternativeembodiment of the mould body 33 for use in manufacturing theencapsulated climbing rung 9 according to the alternative method. Themould body 33 is provided with an upper runner 53 and a lower runner 54.The lower runner comprises runner gates 56. An upper cam 57 is capableof reciprocating the position of an upper ejection system 59. In FIG. 9,the upper ejection system 59 is shown gripping the circumference of eachcore leg 13 of the climbing rung. An annular seal 61 is formed at thecircumference of each core leg 13 when it is gripped by the ejectionsystem 59, thereby sealing the lower portion 63 of the mould cavity 32.At this stage, molten polyethylene flows through the lower runner 54 andenters the lower portion 63 of the mould cavity 32 through the runnergates 56. Injection moulded sleeves 18 are thereby formed, encapsulatingthe end of each core leg 13. The upper cam 17 is then rotated toreciprocate the upper ejection system 59 to a position flush with thesurface 45 of the mould cavity 32, best seen as position 59a in FIG. 10.A lower cam 65 is capable of reciprocating the position of a lowerejection system 67. In FIG. 9 the lower ejection system 67 is shownretracted to a position 67a flush with the surface of the lower portion63 of the mould cavity 32.

Referring to FIG. 10, the lower ejection system 67 is shown gripping thesleeves 18 after the sleeves 18 have been injection moulded. At thissecond stage molten polyethylene flows through the upper runner 53 andenters the upper portion 69 of the mould cavity 32 through the runnergates 55. The molten polyethylene flows into the entire upper cavity 69,evenly coating the central tread 15 and the portion of each core leg 13extending to proximate the annular lip 28 of the sleeves 18, meldingwith each sleeve 18 proximate its annular lip 28 to form a sealinginterface 31 (best seen in FIG. 3). The lower cam 65 is then rotated toreciprocate the lower ejection system 67 to a retracted position 67a(best seen in FIG. 9). The two sections 35,37 (best seen in FIGS. 5 and6) of the mould body 33 may then be separated and the encapsulatedclimbing rung 9 removed from the mould.

It will be appreciated that the core 10 of the climbing rung 9 maythereby be centrally positioned in the mould cavity 32 without grippingthe rung 9 by a pre-formed coating or sleeve 17 --advantageously lesshandling of the rung 9 in its manufacture is thereby achieved.

In another embodiment the steps may be reversed, whereby the injectionmoulded protective sleeves 28 are formed last. All that is necessary isthat the core 10 of the climbing rung be gripped at a position oppositethe portion of the climbing rung to be positioned in the mould cavity63,69.

As many changes can be made to the embodiment of the invention withoutdeparting from the scope of the invention, it is intended that allmaterial be considered as illustrative of the invention and not in alimiting sense.

The embodiments of the invention in which an exclusive property orprivilege is claimed are as follows:
 1. An improved method ofmanufacturing a climbing rung in a mould body having an ejection halfand an injection half, the climbing rung having a generally U-shapedcore of two parallel legs spaced apart by a central tread encapsulatedin a protective coating comprising the combination in a sealinginterface of a pair of pre-formed protective sleves and an injectionmoulded protective coating, the method comprising the steps of (a)sheathing the end of each leg in a pre-formed protective sleeve open atone end to receive the leg; (b) gripping the preformed protectivesleeves with means for gripping the climbing rung only proximate the endof each leg; (c) positioning with the gripping means the tread and legsof the climbing rung extending only to proximate the receptive end ofeach pre-formed protective sleeve centrally in a disjointed injectionmould cavity; (d) closing the ejection half and the injection half ofthe mould body so as to form the mould cavity enclosing the tread andlegs of the climbing rung extending only to proximate the receptive endof each pre-formed protective sleeve, the mould body forming an annularseal at the outside circumference of each pre-formed protective sleeveproximate the receptive end; (e) injecting a molten thermoplasticmaterial into the mould cavity whereby the material flows into theentire mould cavity evenly coating the core of the climbing rung andweeping into the interface at the receptive end of each pre-formedsleeve and each leg, whereby the injected thermoplastic material meldswith the pre-formed protective sleeves to form a sealing interface. 2.An improved method of manufacturing a climbing rung in a mould bodyhaving an ejection half and an injection half, the climbing rung havinga generally U-shaped core of two parallel legs spaced apart by a centraltread encapsulated n a protective coating comprising the combination ina sealing interface of a pair of pre-formed protective sleeves and aninjection moulded protective coating each sleeve having an annular spacebetween the receptive end of said sleeve and the outside annularcircumference of each leg, the method comprising the steps of (a)sheathing the end of each leg in a pre-formed protective sleeve open atone end to receive the leg; (b) gripping the pre-formed protectivesleeves with means for gripping the climbing rung only proximate the endof each leg; (c) positioning with the gripping means the tread and legsof the climbing rung extending only to proximate the receptive end ofeach preformed protective sleeve centrally in a disjointed injectionmould cavity; (d) closing the ejection half and the injection half ofthe mould body so as to form the mould cavity enclosing the tread andlegs of the climbing rung exceeding only to proximate the receptive endof each pre-formed protective sleeve, the mould body forming an annularseal at the outside circumference of each pre-formed sleeve proximatethe receptive end; (e) injecting a molten thermoplastic material intothe mould cavity whereby the material flows into the entire mould cavityevenly coating the core of the climbing rung and weeping into theannular space between the receptive end of each preformed sleeve and theoutside annular circumference of each leg and over the annular lip ofthe receptive end of each pre-formed sleeve and, whereby the injectedthermoplastic material melds with the pre-formed sleeves to form asealing interface.
 3. An improved method of manufacturing anencapsulated climbing rung in a mould body having an ejection half andan injection half, the climbing rung having a generally U-shaped core oftwo parallel legs spaced apart by a central tread encapsulated in aprotective coating, the coating including the combination in a sealinginterface of (i) a pair of injection moulded protective sleevesencapsulating the portion of each leg extending from the end thereof toa position intermediate the end of each leg and the central tread, and(ii) an injection moulded protective coating; encapsulating the treadextending to the sealing interface proximate the annular end of eachinjection moulded protective sleeve remote from the end of each leg; themethod comprising the steps of: (a) gripping with gripping means,alternately one portion and then an oppositely spaced portion of thecore of the climbing rung remote a portion of the core to be positionedwith the gripping means centrally in an injection mould cavity; (b)encapsulating one portion of the core of the climbing rung thus definingan annular encapsulated end thereof when the opposite portion of theclimbing rung is gripped by remotely spaced gripping means, (c) thengripping the most recently encapsulated portion of the climbing rung andencapsulating the oppositely spaced portion of the core of the climbingrung, the later encapsulated portion melding in a sealing interface withthe annular end of the previously encapsulated portion whereby byalternately gripping at least two oppositely spaced portions of the coreof the climbing rung the entire core of the climbing rung is coated inan injection moulding process.
 4. An improved method of manufacturing anencapsulated climbing rung in a mould body having an ejection half andan injection half, the climbing rung having a generally U-shaped core oftwo parallel legs spaced apart by a central tread encapsulated in aprotective coating, the coating comprising the combination in a sealinginterface of i) a pair of injection moulded protective sleevesencapsulating the portion of each leg extending from the end thereof toa position intermediate the end of each leg and the central tread, andii) an injection moulded protective coating encapsulating the treadextending to the sealing interface proximate an annular end of eachinjection moulded protective sleeve remote from the end of each leg; themethod comprising the steps of: (a) gripping the core of the climbingrung with means for gripping the climbing rung only remote the end ofeach leg; (b) positioning with the gripping means the end of each leg ofthe climbing rung extending only to proximate the portion of each legremote the end of each leg centrally in a disjointed injection mouldcavity; (c) closing the ejection half and the injection half of themould body so as to form the mould cavity enclosing the end of each legof the climbing rung extending only to the portion of each leg remotethe end of each leg, the mould body remote the end of each leg formingan annular seal at the outside circumference of the core of each leg ofthe climbing rung; (d) injecting a molten material into the mould cavityenclosing the said end portion of each leg of the climbing rung wherebya pair of moulded protective sleeves are formed, each sleeveencapsulating the portion of each leg extending from the end thereof tothe annular end of the sleeve at a position intermediate the end of eachleg and the central tread; (e) ejecting the climbing rung comprising theinjection moulded protective sleeves from the mould cavity and grippingthe injection moulded protective sleeves with gripping means forgripping the climbing rung only proximate the end of each leg; (f)positioning, with the gripping means for gripping the climbing rung onlyproximate the end of each leg, and the tread centrally in an injectionmould cavity; (g) closing the ejection half and the injection half ofthe mould body so as to form the mould cavity enclosing the tread andeach leg of the climbing rung extending only to proximate The annular ofeach injection moulded protective sleeve, the mould body forming anannular seal at the outside circumference of each injection mouldedprotective sleeve proximate its annular end; (h) injecting the moltenmaterial into the mould cavity whereby the molten material flows intothe mould cavity evenly encapsulating the core of the climbing rungcomprising the central tread and each leg of the climbing rung extendingto the annular end of each injection moulded protective sleeve andmelding in a sealing interface with the annular end of each injectionmoulded protective sleeve.
 5. An improved method of manufacturing anencapsulated climbing rung in a mould body having an ejection half andan injection half, the climbing rung having a generally U-shaped core oftwo parallel legs spaced apart by a central tread encapsulated in aprotective coating, the coating comprising the combintion in a sealinginterface of (i) a pair of injection moulded protective sleevesencapsulating the portion of each leg extending from the end thereof toa position intermediate the end of each leg and the central tread, and(ii) an injection moulded protective coating encapsulating the treadextending to the sealing interface proximate an annular end of eachinjection moulded protective sleeve remote from the end of each leg; themethod comprising the steps of: (a) gripping the core of the climbingrung with means for gripping the climbing rung only proximate the end ofeach leg; (b) positioning with the gripping means the tread and each legof the climbing rung extending only to proximate the portion of each legremote the end of each leg cenrally in a disjointed injection mouldcavity; (c) closing the ejection half and the injection half of themould body so as to form the mould cavity enclosing the tread and eachleg of the climbing rung extending only to provide the portion of eachleg remote the end of each leg, the mould body forming an annular sealat the outside circumference of the core of each leg remote the end ofeach leg; (d) injecting a molten material into the mould cavity wherebythe molten material flows into the mould cavity evenly encapsulating thecore of the climbing rung comprising the central tread and the portionof each leg remote its end; (e) ejecting the climbing rung comprisingthe encapsulated tread and the portion of each leg remote its end fromthe mould cavity and gripping the encapsulated portion of the climbingrung with gripping means for gripping the climbing run only remote theend of each leg; (f) positioning with gripping means for gripping theclimbing rung extending only to proximate the portion of each leg remotethe end of each leg and proximate the injection moulded coating of thetread and the portion of each leg remote the end of the each legcentrally in an injection mould cavity; (g) closing the ejection halfand the injection half of the mould body so as to form the mould cavityenclosing the end of each leg of the climbing rung extending only toproximate the portion of each leg remote the end of each leg, the mouldbody forming an annular seal at the outside circumference of the portionof the injection moulded coating remote the end of each leg; (h)injecting the molten material into the mould cavity enclosing the saidend portion of each leg of the climbing rung whereby a pair of mouldedprotective sleeves are formed, each sleeve encapsulating the portion ofeach leg extending from the end thereof to the annular end of thecoating remote the end of each leg and melding in a sealing interfacewith the annular end of the coating encapsulating each leg remote itsend.